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High-altitude residence during pregnancy is associated with an increased incidence of preeclampsia. To determine whether uteroplacental blood flow was reduced and pelvic blood flow distribution altered before the onset of hypertension, we measured common iliac (CI), uterine (UA), and external iliac (EI) artery flow velocities (FV), indexes of flow distribution, and blood volume (BV) at week 12, 24, and 36 of pregnancy and 6 mo postpartum in 23 normotensive, 7 preeclamptic, 5 transiently hypertensive, and 3 chronically hypertensive residents of 3,100 m. Normotensive women had a progressive increase in CIFV and UAFV, decrease in EIFV, redistribution of CIFV from the EI to the UA, and increase in BV with advancing pregnancy. Preeclamptic women attained maximal UAFV and redistribution of CIFV from the EI to the UA well before the onset of hypertension and, unlike normotensive women, showed no further increases near term. Plasma volume increment with pregnancy related to the fall in the EIFV/CIFV ratio. Transiently hypertensive women resembled normotensive subjects in the parameters measured, whereas chronically hypertensive subjects resembled preeclamptic subjects. We concluded that preeclamptic vs. normotensive pregnant residents of high altitude had less redistribution of CI flow to the UA and no increase in UA blood flow near term. That these differences were present before the onset of hypertension supports the concept that preeclampsia is characterized by an incomplete vascular adjustment to pregnancy.

To determine whether uterine blood flow was reduced and indexes of pelvic blood flow distribution altered in normotensive pregnancy at high (3,100 m) compared with low altitude (1,600 m), we measured uterine, common iliac, and external iliac artery blood flow velocities and diameters in women during pregnancy and again postpartum. Pregnancy increased uterine artery diameter, blood flow velocity, and volumetric flow at both altitudes. Uterine artery blood flow velocity was greater (69.0 +/- 2.2 vs. 59.4 +/- 3.0 cm/s; P < 0.005) but diameter was smaller at 3,100 m than at 1,600 m (2.5 +/- 0.3 mm vs. 3.4 +/- 0.2 mm; P < 0.005), resulting in volumetric flow that was one-third lower at week 36 of pregnancy (203 +/- 48 vs. 312 +/- 22 ml/min, respectively; P < 0.01). Pregnancy increased common iliac blood flow velocity and decreased external iliac artery blood flow velocity at both altitudes. The uterine artery received a smaller percent of common iliac flow at 3,100 than at 1,600 m (46 +/- 7 vs. 74 +/- 6%; P < 0.005). Gestational age was similar but birth weight was lower at 3,100 m than at 1,600 m. Among subjects at 1,600 m, variation in uterine blood flow velocity correlated positively with infant birth weight. We concluded that reduced uterine blood flow and altered pelvic blood flow distribution during pregnancy at high altitude likely contributed to the altitude-associated reduction in infant birth weight.

Low blood volume (BV) during pregnancy is associated with intrauterine growth retardation and preeclampsia, which are more common at high altitude (HA) than at low altitude. We hypothesized that reduced BV expansion during pregnancy predisposed some women to develop preeclampsia and/or have lower-birth-weight infants at HA. BV was lower in 34 HA residents (3,100 m) than in 22 moderate-altitude residents (1,600 m) while nonpregnant (58.3 +/- 1.2 vs. 72.3 +/- 1.3 ml/kg; P < 0.001) and 36 wk pregnant (69.9 +/- 1.9 vs. 83.3 +/- 3.6 ml/kg; P < 0.01). BV fell between weeks 24 and 36 of pregnancy, and total BV increment with pregnancy was less in women who developed preeclampsia or transient hypertension at HA (n = 12). At HA, total blood and plasma volume expansion and arterial O2 saturation correlated negatively with the highest mean arterial pressure recorded during pregnancy (r = -0.73, P < 0.01 and r = -0.58, P < 0.01, respectively). Total BV and late pregnancy change in BV correlated positively with infant birth weight. We concluded that BV expansion in normotensive pregnancy at HA vs. moderate altitude was similar but that nonpregnant BV was less among HA women, accounting for the low BV in pregnancy. HA women who developed preeclampsia or transient hypertension had less BV expansion, particularly during the third trimester, which was associated with smaller infants.